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Inorganic-organic ionic liquid electrolytes enabling high energy-density metal electrodes for energy storage

journal contribution
posted on 01.12.2016, 00:00 authored by Maria ForsythMaria Forsyth, Gaetan Girard, Andrew Basile, Matthias HilderMatthias Hilder, D R MacFarlane, Fangfang ChenFangfang Chen, Patrick HowlettPatrick Howlett
It has recently been shown, in the case of the bis(fluorosulfonyl)amide (FSI) based ionic liquids, that as the concentration of the alkali metal salt (LiFSI or NaFSI) is increased, the alkali metal cation transference number increases, despite an increase in viscosity and decrease in conductivity. At the same time significant enhancements in electrochemical stability and rate performance of devices are also observed. Here we overview some of the recent findings already in the literature and in addition demonstrate the feasibility of stable, high rate room temperature lithium battery cycling in an electrolyte comprised of 60 mol% LiFSI in a trimethyl, isobutyl phosphonium FSI ionic liquid using a high voltage NMC cathode. We also demonstrate that the high rate cycling of lithium and sodium metal in these phosphonium FSI electrolytes leads to a nanostructured anode deposit and a lowering of the interfacial impedance, suggesting a stable SEI layer formation. Finally, we propose a hypothesis that may explain some of the observations thus made, by which the high alkali ion concentration in these mixed electrolyte systems leads to the effective elimination of the mass transport limitations that are chiefly responsible for the formation of dendrites in traditional electrolytes. This work suggests that a new type of ionic liquid consisting of a mixture of metal cations with organic cations can provide a solution to the instability of the reactive alkali metal anodes and hence enable higher energy density technologies.

History

Journal

Electrochimica acta

Volume

220

Pagination

609 - 617

Publisher

Elsevier

Location

Amsterdam, The Netherlands

ISSN

0013-4686

Language

eng

Publication classification

C Journal article; C1 Refereed article in a scholarly journal

Copyright notice

2016, Elsevier Ltd